1. Field of the Invention
The present invention relates to an electrostatic image developing toner used for an electrophotographic system copying machine and a printer. Particularly, the present invention relates to an electrostatic image developing toner having satisfactory fixing properties usable in a wide fixing temperature range, which does not cause an offset phenomenon, a sheet-wrapping phenomenon or the like when it is fixed by heat roller fixing method which does not use an offset-preventing liquor such as a silicone oil or the like and which provides satisfactory gloss, transparency and anti-blocking properties.
2. Discussion of Background
As disclosed in U.S. Pat. No. 2,297,691, JP-B-42-23910 and JP-B-43-24748, an electrophotographic method generally comprises forming an electrostatic latent image on a photoreceptor containing a photoconductive material by various means, developing the latent image with a toner to provide a powder image, transferring the toner powder image to paper or the like if necessary, and then fixing by heating, pressurizing or solvent vapor. Examples of the heat fixing method include oven fixing method, flash fixing method, pressure fixing method, heat roller fixing method and the like, but it is usual for an electrophotographic copying machine or the like to employ the heat roller fixing method. According to this method, a heat efficiency is quite satisfactory when a toner image is fused on a fixing sheet such as paper, an overhead project sheet and the like, and since fixing can be rapidly effected, this method is quite effective as a fixing method for copying at a high velocity. However, there are problems of causing a sheet-wrapping phenomenon and an offset phenomenon that a part of a toner image is deposited on the surface of a fixing roller since the toner image in heat-melted state is made contact with the surface of a fixing roller under pressure and the part of the toner image deposited on the surface of the fixing roller is transferred to next fixing sheet; thus producing a dirty image on the fixing sheet. Heretofore, in order to prevent the offset phenomenon and the sheet-wrapping phenomenon, the surface of a roller was made of such a material as a silicone rubber or a fluorine-resin excellent in releasability to a toner, and its surface was supplied with such a liquid as a silicone oil having a satisfactory releasability to coat the roller surface with its thin film. However, this method is effective for preventing an offset phenomenon and a sheet-wrapping phenomenon, but has problems of making a fixing device complicated since it requires a device for supplying a liquid, making sheet delivery unsatisfactory due to the presence of a silicone oil when printing on both sides, and making the surface of a sheet for an overhead projector sticky. Therefore, it has been proposed in JP-B-52-3304, JP-B-60-17109, JP-B-57-52574 and JP-B-58-58664 to provide a method for forming the surface of a roller from such a material as a fluorine type resin excellent in releasability to a toner and using a toner containing an olefin type wax such as a low molecular weight polyolefin or a low molecular weight polyethylene, as a method for preventing an offset phenomenon without supplying an offset-preventing liquor such as a silicone oil to the surface of a fixing roller, and also it has been proposed in JP-B-55-6895 to provide a method of using a resin having a wide molecular weight distribution as a binder. However, these methods are effective for preventing the sheet-wrapping phenomenon and the offset phenomenon at a high temperature zone, but they do not provide satisfactory performances in respect of gloss and transparency of a mixed color in the case of using a full color toner.
Also, a method for using polysiloxanes in place of a silicone oil or an olefin type wax, is known.
For example, JP-A-7-120962 discloses a toner using such a polysiloxane as illustrated below in place of an olefin type wax or in combination with an olefin type wax: ##STR2## (X is a polyether group, and ester group or an alkoxy group).
Further, JP-A-9-190009 discloses a toner using a polysiloxane of the formula: ##STR3## (R.sup.1 -R.sup.4 are a C.sub.1 -C.sub.6 alkyl group, and R.sup.5 and R.sup.6 are a C.sub.16 -C.sub.600 saturated hydrocarbon group).
These prior arts provide an improved transparency, but are not satisfactory in respect of anti-blocking properties and a fixing temperature range which does not cause an offset phenomenon.
The present inventors have intensively studied the above mentioned problems, and as a result of the study, they have discovered that above mentioned problems can be solved by using a specific polysiloxane having a higher alkyl group introduced into a side chain. The present invention has been completed on the basis of this discovery.